From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) (using TLSv1 with cipher ADH-CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3vTZ4c3tH8zDq5x for ; Thu, 23 Feb 2017 23:56:48 +1100 (AEDT) Date: Thu, 23 Feb 2017 13:56:43 +0100 From: Michal Hocko To: Vitaly Kuznetsov Cc: Nathan Fontenot , linux-mm@kvack.org, mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, mdroth@linux.vnet.ibm.com Subject: Re: [RFC PATCH] memory-hotplug: Use dev_online for memhp_auto_offline Message-ID: <20170223125643.GA29064@dhcp22.suse.cz> References: <20170221172234.8047.33382.stgit@ltcalpine2-lp14.aus.stglabs.ibm.com> <878toy1sgd.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <878toy1sgd.fsf@vitty.brq.redhat.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed 22-02-17 10:32:34, Vitaly Kuznetsov wrote: [...] > > There is a workaround in that a user could online the memory or have > > a udev rule to online the memory by using the sysfs interface. The > > sysfs interface to online memory goes through device_online() which > > should updated the dev->offline flag. I'm not sure that having kernel > > memory hotplug rely on userspace actions is the correct way to go. > > Using udev rule for memory onlining is possible when you disable > memhp_auto_online but in some cases it doesn't work well, e.g. when we > use memory hotplug to address memory pressure the loop through userspace > is really slow and memory consuming, we may hit OOM before we manage to > online newly added memory. How does the in-kernel implementation prevents from that? > In addition to that, systemd/udev folks > continuosly refused to add this udev rule to udev calling it stupid as > it actually is an unconditional and redundant ping-pong between kernel > and udev. This is a policy and as such it doesn't belong to the kernel. The whole auto-enable in the kernel is just plain wrong IMHO and we shouldn't have merged it. -- Michal Hocko SUSE Labs